The problem for dog owners is that the eggs of the tapeworm can end up on berries and mushrooms in the woods via the fox.
The Veterinary Institute is now advising dog owners not to kiss their pets and to wash their hands on a regular basis.
While it carries out its' research, the Institute is asking dog owners in the areas of Uddevalla, Färgelanda, Munkedal and Vänersborg to de-worm their dogs as a precaution.
Animals can pass on the parasite to humans without themselves becoming sick.
12 foxes have been shot north of Uddevalla where the first case was discovered and are currently being examined.